The purpose of this study was to evaluate the usefulness of MR imaging and to describe the MR imaging findings of pregnancy-associated breast cancer. Materials and Methods: From 2006 to 2013, MR images of 23 patients with pregnancy-associated breast cancer were retrospectively evaluated. MR images were reviewed to evaluate lesion detection and imaging findings of pregnancy-associated breast cancer. MR images were analyzed by using the Breast Imaging Reporting and Data System and an additional MR-detected lesion with no mammographic or sonographic abnormality was determined. Results: MR imaging depicted breast cancer in all patients, even in marked background parenchymal enhancement. Pregnancy-associated breast cancer was seen as a mass in 20 patients and as non-mass enhancement with segmental distribution in 3 patients. The most common features of the masses were irregular shape (85%), non-circumscribed margin (85%), and heterogeneous enhancement (60%). An additional site of cancer was detected with MR imaging in 5 patients (21.7%) and the type of surgery was changed. Conclusion: Pregnancy-associated breast cancer was usually seen as an irregular mass with heterogeneous enhancement on MR images. Although these findings were not specific, MR imaging was useful in evaluating the disease extent of pregnancy-associated breast cancer. Index terms

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